Mercury Lead

Thallium (Tl)

From Wikipedia, the free encyclopediaThallium is a chemical element with symbol Tl and atomic number 81. This soft gray post-transition metal is not found free in nature. When isolated, it resembles tin, but discolors when exposed to air.

Thallium in the periodic table

Symbol

Atomic number

Group

Period

Block

Element category

Post-Transition Metal

Physical properties

Phase at STP

Solid

Density

11.85 g/cm³

Atomic weight

204.38 u

Melting point

577 K
303.85 °C
578.93 °F

Boiling point

1746 K
1472.85 °C
2683.13 °F

Atomic properties

Electronegativity (Pauling Scale)

1.62

Electron affinity

36.4 kJ/mol

Oxidation states

−5, −2, −1, +1, +2, +3
(a mildly basic oxide)

Ionization energies

1	589.4 kJ/mol
2	1971 kJ/mol
3	2878 kJ/mol

Electron configuration

Elektronkonfiguration (shorthand)

[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹

Electrons per shell

2, 8, 18, 32, 18, 3

History

Discovered

1861

Discovered by

William Crookes